1. Field of the Invention
The present invention relates to an ultrasonic rotary drive device which is configured for reducing the wearing of surfaces of an ultrasonic generating portion and a rotary output portion of an ultrasonic motor which are in sliding contact with each other.
2. Description of the Related Art
In normal motors which include a power generating portion and a rotary output shaft that rotates by power generated by the power generating portion, a large adverse influence is exerted on the power generating portion if an unduly large force is transferred to the power generating portion from the rotary output shaft by rotating the rotary output shaft when the power generating portion is not in action.
In contrast, in ultrasonic motors (e.g., Japanese Patent Publication No. 2503997) which include an ultrasonic generating portion and a rotary output portion that is in contact with the ultrasonic generating portion to be rotatable relative to the ultrasonic generating portion, a large adverse influence is not exerted on the power generating portion (ultrasonic generating portion) as compared with the case of normal motors, even if the rotary output portion is rotated when the ultrasonic generating portion is not in action.
However, since an ultrasonic motor is constructed so that the ultrasonic generating portion and the rotary output portion rotate relative to each other while being in sliding contact with each other, points of contact between the ultrasonic generating portion and the rotary output portion wear away if the rotary output portion is rotated when the ultrasonic generating portion is not in action. Therefore, it is also desirable that an ultrasonic motor be constructed so that the rotary output portion does not rotate when the ultrasonic generating portion is not in action.